The King County Council and Seattle City Council both gave the go-ahead for an agreement to build a new professional basketball and hockey arena in Seattle.

The union that represents Longshore workers plans to file a lawsuit to stop it.

The $490-million arena would be built with $200 million in public financing. Hedge fund manager Chris Hansen has been instrumental in pushing the deal. Under the agreement, the public investment would be paid back with rent money and admissions taxes from the arena. If that money falls short, Hansen would be responsible for making up the rest. That detail proved critical for some county council members.

Less impressed is the Longshore Union, which has vowed to file a lawsuit. The union says building another sports venue in the Sodo area will erode maritime, manufacturing and warehousing businesses. King County Councilmember Joe McDermott tried to address those concerns before the vote. He says an environmental review will happen, and other sites will be considered. “This is not a final agreement," said McDermott. "This is an agreement to a process. I’m very proud of the work that this council has done in seeking to afford this cachet, this public value the possible return of the SuperSonics to Seattle.”

International Longshore and Warehouse Union Local 19 attorney David Mann says the memo is a proposal, and should have been subjected to an environmental review. Mann said, “Are they going to turn around a year from now after they’ve gone through the environmental review process and tell Chris Hansen 'no?' Of course not.”

Hansen wants the stadium built near the Mariners and Seahawks stadiums.

The Seattle City Council approved the deal 7-2. The County Council's vote was unanimous.